In the fields of displays for use in television receivers and information terminals, studies have been made for replacing conventionally mainstream cathode ray tubes (CRT) with flat-panel displays which are to comply with demands for a decrease in thickness, a decrease in weight, a larger screen and a high fineness. Such flat panel displays include a liquid crystal display (LCD), an electroluminescence display (ELD), a plasma display panel (PDP) and a cold cathode field emission display (FED). Of these, a liquid crystal display is widely used as a display for an information terminal. For applying the liquid crystal display to a floor-type television receiver, however, it still has problems to be solved concerning a higher brightness and an increase in size. In contrast, a cold cathode field emission display uses cold cathode field emission devices (to be sometimes referred to as “field emission device” hereinafter) capable of emitting electrons from a solid into a vacuum on the basis of a quantum tunnel effect without relying on thermal excitation, and it is of great interest from the viewpoints of a high brightness and a low power consumption.
FIGS. 20 and 21 shows a cold cathode field emission display to which the field emission devices are applied (to be sometimes referred to as “display” hereinafter). FIG. 20 is a schematic partial end view of the display, and FIG. 21 is a schematic partial perspective view of the display when a cathode panel CP and an anode panel AP are disassembled.
The field emission device shown in these drawings is a so-called Spindt type field emission device having a conical electron emitting portion. Such a field emission device comprises a cathode electrode 111 formed on a supporting member 110, an insulating layer 112 formed on the supporting member 110 and the cathode electrode 111, a gate electrode 113 formed on the insulating layer 112, an opening portion 114 formed in the gate electrode 113 and the insulating layer 112, and a conical electron emitting portion 115 formed on the cathode electrode 111 positioned in a bottom portion of the opening portion 114. Generally, the cathode electrode 111 and the gate electrode 113 are formed in the form of a stripe each in directions in which projection images of these two electrodes cross each other at right angles. Generally, a plurality of field emission devices are arranged in a region (corresponding to one pixel, and the region will be called an “overlapped region” or an “electron emitting region” hereinafter) where the projection images of the above two electrodes overlap. Further, generally, such electron emitting regions are arranged in the form of a matrix within an effective field (which works as an actual display portion) of a cathode panel CP.
An anode panel AP comprises a substrate 30, a phosphor layer 31 (31R, 31B and 31G) which is formed on the substrate 30 and has a predetermined pattern, and an anode electrode 33 formed thereon. One pixel is constituted of a group of the field emission devices formed in the overlapped region of the cathode electrode 111 and the gate electrode 113 on the cathode panel side and the phosphor layer 31 which is opposed to the above group of the field emission devices and is on the anode panel side. In the effective field, such pixels are arranged on the order of hundreds of thousands to several millions. On the substrate 30 between one phosphor layer 31 and another phosphor layer 31, a black matrix 32 is formed.
The anode panel AP and the cathode panel CP are arranged such that the electron emitting regions and the phosphor layers are opposed to each other, and the anode panel AP and the cathode panel CP are bonded to each other in their circumferential portions through a frame 34, whereby the display is produced. In an ineffective field (ineffective field of the cathode panel CP in the example shown in the drawings) which surrounds the effective field and where a peripheral-circuit for selecting pixels is formed, a through-hole 36 for vacuuming is provided, and a tip tube 37 is connected to the through-hole 36 and sealed after vacuuming. That is, a space surrounded by the anode panel AP, the cathode panel CP and the frame 34 is in a vacuum state.
A relatively negative voltage is applied to the cathode electrode 111 from an cathode-electrode control circuit 40, a relatively positive voltage is applied to the gate electrode 113 from a gate-electrode control circuit 41, and a positive voltage having a higher level than the voltage applied to the gate electrode 113 is applied to the anode electrode 33 from the anode-electrode control circuit 42. When such a display is used for displaying on its screen, a scanning signal is inputted to the cathode electrode 111 from the cathode-electrode control circuit 40, and a video signal is inputted to the gate electrode 113 from the gate-electrode control circuit 41. Due to an electric field generated when a voltage is applied between the cathode electrode 111 and the gate electrode 113, electrons are emitted from the electron emitting portion 115 on the basis of a quantum tunnel effect, and the electrons are attracted toward the anode electrode 33 and collide with the phosphor layer 31. As a result, the phosphor layer 31 is excited to emit light, and a desired image can be obtained. That is, the working of the display is controlled, in principle, by a voltage applied to the gate electrode 113 and a voltage applied to the electron emitting portion 115 through the cathode electrode 111.
In the above display constitution, it is effective to sharpen the top end portion of the electron emitting portion for attaining a large current of emitted electrons at a low driving voltage, and from this viewpoint, the electron emitting portion 115 of the above Spindt type field emission device can be said to have excellent performances. However, the formation of the conical electron emitting portion 115 requires advanced processing techniques, and with an increase in the area of the effective field, it is beginning to be difficult to form the electron emitting portions 115 uniformly all over the effective field since the number of the electron emitting portions 115 totals up to tens of millions in some cases.
There has been therefore proposed a so-called flat-surface type field emission device which uses a flat electron emitting portion exposed in a bottom portion of an opening portion without using the conical electron emitting portion. The electron emitting portion of the flat-surface type field emission device is formed on a cathode electrode, and it is composed of a material having a lower work function than a material constituting the cathode electrode for achieving a high current of emitted electrons even if the electron emitting portion is flat. In recent years, it has been proposed to use various types of carbon materials such as diamond-like carbon (DLC) as the above material.
That is, for example, in Lecture No. 2p-H-6 on page 631 of preprints of No. 60 Applied Physics Society Lectures (1999), there is disclosed a flat-surface-structured electron emitter obtained by scratch-processing a surface of a titanium thin film formed on a quartz substrate by an electron beam deposition method, with a diamond powder, then patterning the titanium thin film to form a several μm gap in a central portion, and then, forming a non-doped diamond thin film on the titanium thin film. In Lecture No. 2p-H-11 on page 632 of preprints of No. 60 Applied Physics Society Lectures (1999), there is disclosed a method in which a carbon nano-tube is formed on a quartz glass provided with a metal cross line.
The value of a voltage (threshold voltage) at which electrons begin to be emitted from an electron emitting portion can be decreases by usage of various carbon-containing materials including diamond-like carbon. However, a gas or gaseous substance released from various members constituting the cathode electrode and the display adheres to, or is adsorbed on, the electron emitting portion, and as a result, the electron emitting portion is deteriorated in properties, which is known, for example, in the literature of MRS 2000 Spring Meeting, Preprints Q1.3/R1.3, page 264 “SURFACE MODIFICATION OF Si FIELD EMITTER ARRAYS FOR VACUUM SEALING”. The above literature reports that the formation of a carbon thin film on the surface of a silicon-based electron emitting portion can inhibit the adherence and adsorption of the gas or gaseous substance to/on the electron emitting portion.
However, the above literature does not suggest any means of overcoming the problem of adherence and adsorption of a gas or gaseous substance to/on the electron emitting portion made from a carbon-containing material.
It is therefore an object of the present invention to provide an electron emitting apparatus and a cold cathode field emission device that can overcome the problem that a gas or gaseous substance released from various members constituting, for example, a cold cathode field emission display adheres to, or is adsorbed on, an electron emitting portion to cause the electron emitting portion to deteriorate in properties, manufacturing methods of these, and a cold cathode field emission display to which the above cold cathode field emission device is incorporated and a manufacturing method thereof.